Utilized complex circular correlational statistics to determine that the hue associated with a letter is strongly correlated with the frequency of that letter in written language

Repeated correlational analyzes across three languages and three distinct groups of synesthetes

Ruled out other possible influences, such as letter order, color term frequency, and cultural biases, via supplementary studies

Integrated findings into current developmental accounts of synesthesia: the findings help to explain the cause of individual grapheme-color associations and suggests that synesthetes’ exposure to written language guides the grapheme–color associations that they form.

Bolstered previous neurophysiological data, which suggested excess neural connections between cortical area V4 and the visual word form area in synesthetes, due to the neuroanatomy of these areas, organized by color hue and letter frequency

Provided the first large-scale collection of Spanish-speaking synesthetes’ letter-color associations.

Results:

Presentations at the American Academy of Neurology Annual Meeting, the Vision Sciences Society Annual Meeting, the International Conference for Cognitive and Neural Systems, the American Junior Academy of Science, the UK Synesthesia and Cross-Modal Perception conference, the American Synesthesia Association Conference, and President Obama's White House Science Fair

Figure 1. Letter frequencies and associated colors. The letters are ordered from most frequent (left) to least frequent (right). The letters are shaded in the hue most commonly associated with that color. For example, nearly every German synesthete sees “N,” one the most common letters in the German language, as red (Emrich, Schneider, Zedler, 2004). On the other hand, most English-speaking synesthetes see “N," a moderately frequent letter in English, as green. (Some letters are excluded due to their predominant hue being indeterminate, such as brown or gray.)

Table 1. Circular correlation between hue and letter frequency.Includes the correlation and p values for the circular correlation between each language’s letter frequencies and each language’s associated color hues.